In the lithography technology, a highlight is recently put on the organic solvent development again. It would be desirable if a very fine hole pattern, which is not achievable with the positive tone, is resolvable through negative tone exposure. To this end, a positive resist composition featuring a high resolution is subjected to organic solvent development to form a negative pattern. An attempt to double a resolution by combining two developments, alkaline development and organic solvent development is under study.
As the ArF resist composition for negative tone development with organic solvent, positive ArF resist compositions of the prior art design may be used. Such pattern forming processes are described in Patent Documents 1 to 3. These patent documents disclose resist compositions for organic solvent development comprising a copolymer of hydroxyadamantane methacrylate, a copolymer of norbornane lactone methacrylate, and a copolymer of methacrylate having acidic groups including carboxyl, sulfo, phenol and thiol groups substituted with two or more acid labile groups, and pattern forming processes using the same.
Further, Patent Document 4 discloses a process for forming a pattern through organic solvent development in which a protective film is applied onto a resist film. Patent Document 5 discloses a topcoatless process for forming a pattern through organic solvent development in which an additive is added to a resist composition so that the additive may segregate at the resist film surface after spin coating to provide the surface with improved water repellency.
When trench patterns (isolated space patterns) or hole patterns are formed by the positive tone development process using an alkaline aqueous solution, pattern formation must be done with incident light of a weak intensity as compared with formation of line or dot patterns. Then the contrast of intensity of incident light between exposed and unexposed regions becomes low. The low contrast is likely to impose limits on the pattern forming abilities like resolution, tending to bring difficulty in forming a resist pattern at a high resolution. As opposed to the positive tone development process, the organic solvent development process is believed advantageous for forming trench or hole patterns. This is one of the reasons why a highlight is recently put on the organic solvent development.
However, the organic solvent development process has some problems to be overcome. The positive development system involving deprotection reaction to generate a carboxyl group and subsequent neutralization reaction with aqueous alkaline developer to improve a dissolution rate achieves a high dissolution contrast in that the dissolution rate differs between the unexposed and exposed regions by a factor of more than 1,000. In contrast, the negative development system via organic solvent development provides a low contrast because the dissolution rate in the unexposed region due to solvation is low, and the dissolution rate thus differs between the unexposed and exposed regions by a factor of less than 100. For the negative development system via organic solvent development, it is desired to seek for a novel material which can enhance a dissolution contrast.